The present invention is generally directed to power supplies for electronic equipment which is to be supplied from three-phase power sources. More particularly, the present invention is directed to a power supply containing a plurality of power conversion units which are capable of three-phase power switching. Even more particularly, the invention is directed to a power supply configuration which is resistant to failure in one of the converter units.
When electronic or other equipment must be provided with more than three kilowatts of electric power, it becomes very convenient, if not necessary, to employ three-phase power input sources. Typically, in three-phase power supply units, three separate converter units are employed in either a delta or wye connection. There is, however, a greater probability of failure present in such systems merely because a failure can occur when any one of the converters and/or regulators employed fails. Accordingly, it is desirable to provide a mechanism for continued appropriate operation in the event of a single converter unit failure.
Similar systems have been designed which provide three-phase power supplies which continue operation even after the failure of a single one of the supply phases. In such circumstances, the solution proffered has been the opening of switches which shut down the power supply portion in that particular unit. However, this is not always desirable and it would certainly be preferable to continue operation of the unit where appropriate. However, in the event of failure in one of the phases, this is not possible. However, in circumstances in which reliability issues are directed to failure of the converters or regulators themselves, it is possible, in accordance with the present invention, to provide circuits to perform a phase switching operation as opposed to completely shutting down the subject unit.
Additional power supply design concerns are also addressed by the present invention. In particular, when a converter failure occurs, and particularly, when only two converters are carrying the load instead of three, this results in an unbalanced load since, in effect, one leg of a delta-connected converter is open. The resulting line current will therefore increase significantly in one of the three phases. The increased current drawn during such conditions would force circuit designers to construct power feed circuits which are sized for the higher currents which are typically seventy-five percent higher than would otherwise be seen. This aspect has two negative consequences. Firstly, it results in a higher power system cost. Secondly, because of the higher current requirements, it may require an end user to upgrade power feed requirements to higher levels than would otherwise be needed.
The AC/DC power converters described herein are preferably arranged in a so-called N+1 configuration wherein each unit includes a DC power converter and wherein N+1 units are connected in a delta configuration. While the power converter is configured to receive three-phase power, normal operation only involves a single phase pair. When one of the N+1 converter units fails, system availability of bulk power is assured as N converters are still operational and are available to provide power to the load. However, when converter failure does occur, the remaining operational converters experience increased power demands since fewer units are available to carry the load. The redundancy feature is an important aspect for providing overall system reliability. This is particularly true when the power supplies are being used to run large computer systems, where the demands for reliability and availability are high.
When one of the N+1 converters fails in such a configuration, the load is still assured of bulk power as N converters are still operational. In order to maintain bulk power, it is necessary for the two operational converters to provide an increased level of power which compensates for the loss of the third converter. Although bulk power can generally be maintained, one leg of the delta-connected converter is open and the input views the delta connection as an unbalanced load. As a result, the line currents on one of three lines will increase significantly in order to maintain power. More importantly, however, it is possible that the current imbalance will cause an upstream three-phase circuit breaker to trip, thus causing a system outage. In terms of reliability and/or availability, this is not by any means a desirable event. Accordingly, it is very desirable to have a regulator and/or converter configuration which is self-balancing during the failure of one of the regulators.